Classification of Alcohol, Phenol and Ether

Alcohol, phenol and ether are classes of organic compounds that incorporate the C⎯O bond. The alcohol, phenol and ether functional groups are found in many important naturally occurring molecules like glucose, glycerol, cholesterol. They have many applications in several domestic and industrial processes. So, let's get started with the classification of alcohol in chemistry, classification of phenol, what are ethers, how are they classified, and their uses.


Alcohols

Alcohols contain the hydroxyl (⎯OH) functional group connected to a carbon atom by a covalent bond. Alcohols include all compounds having the general formula CnH2n+1OH. Examples – ethyl alcohol, methyl alcohol, butyl alcohol, etc.


Classification of Alcohol

Alcohols can be classified into three types depending on the number of carbon atoms directly bonded to the carbon atom containing the hydroxyl functional group. The types are:

  • Primary alcohol (1°): The carbon atom carrying the hydroxyl group is attached to only one alkyl group. Example: 1-butanol, 2-methyl-1-propanol.

  • Secondary alcohol (2°): The carbon atom carrying the hydroxyl group is attached to two alkyl groups, either the same or different. Example: 2-butanol.

  • Tertiary alcohol: The carbon atom carrying the hydroxyl group is attached to three alkyl groups, all the same, or different. Example: 2-methyl-2-propanol.

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Another classification of alcohols is based on the number of hydroxyl groups attached. The three types under this classification are:

  • Monohydric Alcohol: Alcohols containing one hydroxyl group. Example: CH3-CH2-OH (Ethanol), CH3-CH2-CH2-OH (Propanol).

  • Dihydric Alcohol: Alcohols containing two hydroxyl groups. Example: 1, 2-Ethanediol, 1, 3-Propandiol.

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  • Trihydric Alcohol: Alcohols containing three hydroxyl groups. Example: 1, 2, 3-Propantriol, 1, 2, 3-Butantriol.

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Uses of Alcohol

  • Ethyl alcohol is the major component of alcoholic drinks like wine and beer.

  • Ethanol, combined with a small quantity of methanol, is sold as a methylated spirit with many industrial applications.

  • Ethanol combustion produces energy, carbon dioxide, and water and can be used by itself or with petrol as a fuel.

  • Ethanol is widely used as a solvent for dissolving organic compounds and is used in the manufacture of perfumes and cosmetics.

  • Methanol is combined with petrol to improve combustion.

  • Methanol serves as an industrial feedstock for the preparation of other compounds like aldehydes and acids.


Phenols

Phenols are compounds in which the ⎯OH group is directly attached to an aromatic ring and are designated as ArOH. Phenol differs from alcohol in that the former is slightly acidic in water and reacts with aqueous sodium hydroxide to form salts. Example: C6H5OH, the parent compound, is called phenol.


Classification of Phenol

Phenols can be classified into the following categories depending on the number of hydroxyl groups present:

  • Monohydric Phenol: Contain only one hydroxyl group. Example: C6H5OH (phenol)

  • Dihydric Phenol: Contain two hydroxyl groups. Example: Benzene-1, 2-diol.

  • Trihydric Phenol: Contain three hydroxyl groups. Example: Benzene-1, 3, 5-triol.

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Uses of Phenol

  • Phenols are widely used as an antiseptic and disinfectant.

  • Phenol is a useful precursor for the synthesis of food preservatives, pharmaceuticals, resins, polymers, and adhesives.

  • Phenolics are components of many biological systems and are present in naturally occurring substances like flavouring agents, neurotransmitters, and vitamins.

  • Bisphenol A is a component of polycarbonate plastics.


Ethers

Ethers are the class of organic compounds containing the functional group ⎯O⎯. Ethers have the general formula R⎯O⎯R, where the hydrocarbon groups (R) may be either the same or different.


Classification of Ether

Ethers are classified into the following two types based on the type of alkyl or aryl groups attached to the ⎯O⎯.  functional group. The types are:

  • Symmetrical ethers or simple ethers: These ethers have the same alkyl or aryl groups attached on either side of the ⎯O⎯ functional group. Example: C2H5⎯O⎯C2H5 (diethyl ether), CH3⎯O⎯CH3 (dimethyl ether).

  • Unsymmetrical ethers or mixed ethers: These ethers have different alkyl or aryl groups attached on either side of the ⎯O⎯functional group. Example: C2H5⎯O⎯CH3 (ethyl methyl ether), CH3⎯O⎯C6H5 (methyl phenyl ether). 


Uses of Ether

  • Dimethyl ether is used as a refrigerant and as a solvent at low temperatures.

  • Diethyl ether is used as a universal solvent for gums, oils, and resins.

  • Diethyl ether is also a common anesthetic ingredient in surgery.

  • Due to its high boiling point, phenyl ether serves as a heat transfer medium.

  • Methoxybenzenes are used in cosmetics, pharmaceuticals, and are naturally present in insect pheromones.

FAQ (Frequently Asked Questions)

1. How are Alcohols and Ethers Named?

Ans: 

- Guidelines for Naming Alcohols:

  • Find the longest carbon chain containing the hydroxyl group.

  • Start numbering from the end of the chain closest to the hydroxyl group. In a molecule containing both the ⎯OH group and multiple bonds, the carbon having the attached ⎯OH group is assigned the lowest possible number.

  • Remove the last 'e' from the parent alkane name and add the suffix –ol. Use 'di,' 'tri, etc. for multiple alcohol groups. Examples:

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- Guidelines for Naming Ethers:

  • The alkyl groups attached to ⎯O⎯  are named alphabetically as two distinct words, and the term 'ether' is added. The prefix 'di' is added if the two groups attached to ⎯O⎯ are the same.

  • Alternatively, the alkoxy group is used as a substituent on the alkane backbone while the stem of the ether name comes from the longest continuous alkyl chain. Examples:

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2. What are Some of the Properties of Alcohols, Phenols, and Ethers?

  • The oxygen atom in alcohol has sp³ hybridization with two nonbonding pairs of electrons.

  • Alcohols are strongly polar due to the oxygen-hydrogen bonds. The large electronegativity difference between oxygen and hydrogen atoms imparts the polarity. Thus, alcohols undergo intra as well as intermolecular hydrogen bonding.

  • Hydrogen bonding has two consequences: alcohols have comparatively higher boiling points than organic compounds of similar molecular weight, and alcohols are significantly more soluble in water than other organic compounds.

  • Ethers have weak intra-molecular dipole-dipole interactions; they are not hydrogen bond donors and hence insoluble in water.

  • The non-reactive nature of ethers makes them useful solvents.

  • Phenols also exhibit hydrogen bonding and are partially soluble in water.

  • Alcohols strongly absorb radiation in the infrared region (~3500 cm⁻¹).